1. Field of the Invention
The present invention relates to an image forming apparatus such as a digital copier or laser printer, and more particularly to a jam disposal mechanism that allows a paper jam to be disposed of from the side of a fixing unit.
2. Description of Related Art
The construction of a conventional image forming apparatus is shown in FIG. 8. Reference numeral 100 represents an image forming apparatus, which is here assumed to be a digital multifunctional product, for example. When the image forming apparatus 100 performs a copying operation, in an image forming section P arranged above a conveying belt 9 inside the cabinet of the multifunctional product, steps of charging, exposure, development, and transferring are performed to form a predetermined image based on original image data read by an image reading section 6.
In the image forming section P, a photoconductor drum 2 for carrying a visible image (toner image) is arranged. The toner image formed on the photoconductor drum 2 is transferred to a sheet (recording medium) 7 carried and conveyed by a transfer belt 9 that moves adjacently to the image forming section P. The transferred toner image is then fixed on the sheet 7 in a fixing unit 8, and is then ejected out of the cabinet of the apparatus. While the photoconductor drum 2 is rotated clockwise (in the direction indicated by arrow A) as viewed in FIG. 8, an image forming process is performed with respect to the photoconductor drum 2.
Next, the image forming section P will be described in detail. The photoconductor drum 2 is arranged so as to be freely rotatable. Around and above the photoconductor drum 2, there are provided: a charger 3 for electrically charging the photoconductor drum 2, an exposure unit 4 for exposing the photoconductor drum 2 to light representing image information; a developer unit 5 for forming a toner image on the photoconductor drum 2; and a cleaning section 10 for removing developing agent (toner) that remains on the photoconductor drum 2.
The surface of the photoconductor drum 2 is first electrically charged uniformly by the charger 3, and is then exposed to light by the exposure unit 4 so that an electrostatic latent image according to an image signal is formed on the photoconductor drum 2. The developer unit 5 is loaded with a predetermined amount of toner by a toner container 11. This toner is fed by the developer unit 5 onto the photoconductor drum 2 so as to be electrostatic ally adhered to the surface thereof, on which a toner image is thus formed according to the electrostatic latent image formed through the exposure by the exposure unit 4.
The sheet 7 to which the toner image is transferred is housed in a sheet housing section 12, which is composed of a plurality of paper feed cassettes 12a, 12b, and 12c and a stack bypass (hand-feed tray) 12d provided above them. The sheet is fed via paper feed rollers 13 and resist rollers 14 onto the conveying belt 9 so as to be conveyed into position on the photoconductor drum 2. The paper feed cassettes 12a, 12b, and 12c are detachably attached to the apparatus cabinet 1.
The conveying belt 9 is hung around and between a drive roller 15, disposed downstream, and a follower roller 16, disposed upstream. When the conveying belt 9 starts to rotate counter-clockwise, the sheet 7 is conveyed via the resist rollers 14 onto the conveying belt 9. At this time, an image write signal turns on, so that an image is formed on the photoconductor drum 2 with predetermined timing.
Under the photoconductor drum 2, a transfer roller 17 is arranged to which a predetermined transfer voltage is applied. At the nip between the photoconductor drum 2 and the transfer roller 17, the toner image on the photoconductor drum 2 is transferred to the sheet 7. The sheet 7 is held on the conveying belt 9 by electrostatic attraction. The conveying belt 9 is formed of a dielectric resin sheet, and is built as an endless or seamless belt by joining together opposite ends of such a sheet.
The sheet 7 having the toner image transferred thereto is separated from the conveying belt 9, and is conveyed to the fixing unit 8. On the other hand, after the transfer of the toner image, the photoconductor drum 2 is cleaned by the cleaning section 10 so that the toner that remains on the surface of the photoconductor drum 2 is removed in preparation for the subsequent formation of a new electrostatic latent image. Conveyed from the conveying belt 9 to the fixing unit 8, the sheet 7 is then heated and pressed by a pair of fixing rollers 8a and 8b so that the toner image is fixed on the surface of the sheet 7 to form a predetermined image. Having the image formed thereon, the sheet 7 then passes via pairs of conveying rollers 18 and 19, and is then ejected by a pair of ejection rollers 20 onto an ejected paper tray 21.
Although not illustrated, a charge removing device for removing the residual electric charge on the surface of the photoconductor drum 2 is provided on the downstream side of the cleaning section 10. Reference numeral 22 represents a cover provided on a side face of the apparatus cabinet 1. The cover 22 is so built as to be freely openable and closable in the direction indicated by arrow B about a pivot 23. Opening this cover 22 allows simple maintenance work, such as removable of a paper jam.
In the image forming apparatus constructed as described above, if the sheet 7 is stuck in the middle of image formation and causes a paper jam, for example, extracting the fixing unit 8 out of the apparatus cabinet 1 parallel to the paper conveying direction (that is, leftward in FIG. 8) makes it possible to dispose of the paper jam. Inconveniently, however, doing so involves pulling out the sheet 7 held between the photoconductor drum 2 and the transfer roller 17, and this may cause various problems, such as the sheet 7 breaking, or the unfixed toner splashing and soiling the interior of the apparatus.
To overcome this inconvenience, for example, JP-A-2002-72819 proposes an intermediary-transfer-type image forming apparatus wherein at least a secondary transferring member and fixing means are held with a holding member and wherein this holding member is so built as to be freely extractable in a direction that points away from the image forming apparatus and that coincides with the paper ejection direction. Certainly, this makes it possible to remove a jammed sheet without breaking it or soiling the interior and exterior of the apparatus with unfixed toner.
With the technique disclosed in JP-A-2002-72819 mentioned above, however, it is necessary to provide a holding member for holding at least the fixing unit 8 and the transfer roller 17. In this case, for the holding member to be able to hold the fixing unit 8 and the transfer roller 17, the holding member itself needs to be considerably large. Disadvantageously, this unduly increases the size and cost of the image forming apparatus. Moreover, to dispose of a paper jam, it is necessary to extract the holding member along with the fixing unit 8 and the transfer roller 17 it holds. Disadvantageously, this requires a wider work space than extracting the fixing unit 8 alone.